In view of the depletion of fossil fuels and the prevention of a global warming, introduction of power generation systems utilizing natural energy (e.g., wind power and solar power) is advancing worldwide. A wind power generation device converts energy possessed by wind into rotation energy through a wind turbine, and transmits such energy to a power generator directly or with an increase in the rotation speed by a speed-up gear, thereby generating electrical energy. A wind farm is a system for generating large power by placing wind power generation devices of several tens to a hundred or more on a broad land or on the broad ocean.
When the scale increases, a wind farm affects a stable operation of a power system, and thus an output control performance and a system interconnection management equivalent to those of a thermal power generation plant are required. System interconnection requirements to interconnect a wind farm with a commercial system are defined by respective electric power companies and national standards which are disclosed in, for example, “System Connection Technology Requirement of Wind Power Generation Facilities (for extremely high voltage)”, Dec., 2011, Tohoku-Electric Power Co., Inc.; and Standard Number IEC61400-25-2 (Wind Turbines-Part 25-2: Communications for monitoring and control of wind power plants-Information models) Annex C, 2006-12-14.
In a power system, a thermal power generation device or a water power generation device controls respective frequencies within a certain range, and when a wind farm that changes the frequency in accordance with wind is interconnected with the power system, the load of frequency control increases. During a night at which the thermal power generation devices and the water power generation devices in the power system are deactivated, the frequency maintaining performance decreases, and thus it may be necessary in some cases to parallel off the wind farm.
The fluctuation originating from the wind farm also causes a voltage fluctuation at a connection point, which deteriorates the power quality. The above standard IEC61400-25-2 also defines a spinning reserve to be held, i.e., a performance that can increase supplied power to a system when a disturbance like a breakdown occurs in an interconnected power system. By maintaining the spinning reserve, the wind farm can be operated as a power plant that can contribute to the system stabilization.
For a power producer possessing a wind farm, it becomes possible to increase the operating rate while avoiding unnecessary parallel off, and further to contribute to the system stabilization when a breakdown of a power system occurs by controlling the wind farm output so as to satisfy the system interconnection requirement. Hence, JP 2009-239990 A, JP 2007-32488 A, and JP 2007-37226 A disclose wind farm control technologies, but those control technologies are not made in consideration of maintaining a spinning reserve. Moreover, Japan Patent No. 4881349 discloses a wind-farm-output control technology of adjusting the output by a wind farm so as to maintain a reserved power.
There are needs for power producers to not only maintain a spinning reserve while satisfying a system interconnection requirement, but also stabilize the yieldability by maximally utilizing wind energy to perform an efficient operation. The wind farm operation technology of Japan Patent No. 4881349 enables an operation of a wind farm that maintains a reserved power while satisfying a system interconnection requirement. However, Japan Patent No. 4881349 does not explicitly describe a specific way to realize the distribution method of the outputs of respective wind power generation devices. Therefore, it cannot be always said that the efficiency of the method of Japan Patent No. 4881349 is the best. Moreover, when the frequency increases, a wind farm output can be reduced and suppressed, but when the frequency decreases, it is difficult to increase the output.